Why is engine so insistent that I retreat my bishop?

I think it has to do with the g4 square and not the bishop that is on that square.
Your knight cannot move to g4 while your bishop is on that square.

i believe dale is correct. it wants to free that square. also going to e6 makes black need to waste a tempo to protect the a pawn before they can move the rook.
Sorry man but this game is terrible.Like first you sac your bishop without any sense.Then you played 10..Dd4? instead of simple Qxb2.I don't want even comment 20..Rf2??.and then you ask why engine retreat a bihop.It would be probably better for you to ask:"Why my opponent played so stupid?"